The passively mode-locked type-I quantum well cascade diode lasers operating near 2.7 and 3.2 m generated trains of the 10 ps long pulses with average power up to 10 mW. The devices based on laser heterostructures with reinforced carrier confinement requires increased reverse bias voltages applied to absorber sections to operate in mode-locked regime. The autocorrelation measurements showed that lasers generated strongly chirped pulses with temporal width an order of magnitude above transform limit. The application of the external feedback led to narrowing of the laser emission spectra accompanied by an order of magnitude reduction of the intermodal beat note linewidth. The multiheterodyne beat notes have been observed for devices stabilized by external feedback. 1983-2012 IEEE.